This invention relates to a process for the electrolytic oxidation of sodium dialkyldithiocarbamates to tetraalkylthiuram disulfides.
Tetraalkylthiuram disulfides are commerically important in industry and agriculture as, for example, vulcanization accelerators, fungicides, and seed treating agents. The usual industrial method of making these compounds involves oxidation of dialkyldithiocarbamates with chlorine. Because of overoxidation, which cannot be avoided, the yield of the chlorine oxidation process does not exceed about 88%. The overoxidation products, large quantities of sodium chloride, and a small amount of the thiuram disulfide are removed in the waste stream.
Electrolytic oxidation of dialkyldithiocarbamates to tetraalkylthiuram disulfides theoretically appears to be a much better alternative since it should be capable of producing purer product in a higher yield and would not present as environmentally serious waste disposal problems as does the chlorine oxidation method. The electrochemical reaction has been attempted in the past but without much success. Thus, U.S.S.R. Pat. No. 53,766 (1938) discloses a process for the continuous electrolysis of sodium dimethyldithiocarbamate using a scraped, rotating nickel anode. A thin sheet of asbestos is inserted between the anode and the cathode, but its purpose is not explained in the patent. The necessity of using a rotating anode is a serious shortcoming of this process because it usually is difficult to maintain good chemical contact between a rotating electrode and the source of electrical current. Apparently the combination of rotating anode and a scraper, which removes the product, avoids excessive build-up of the product on the anode.
U.S. Pat. No. 2,385,410 (1945) describes an electrolytic process using alternating current to avoid deposition of the product on the electrodes. Direct current electrolysis requiring scraped electrodes is said to be awkward and inconvenient. The product appears, however, to have been obtained in low yield and in a state of questionable purity. Because, according to the patentee, a neutral medium is preferred, pH control is important. Acid is added gradually to the cell to neutralize caustic generated during the electrolysis.
It can be seen that the electrochemical production of tetraalkylthiuram disulfides from dialkyldithiocarbamates has not lived up to the expectations, and that an improved process would be very desirable.